Polymerization alkadienes

V. Mark and E. N. Peters, Polycarbonate exhibitir improved impact properties containing divalent residue of polymerized alkadiene monomer, U.S. Patent 4,728,716 (1988). 

Depending on the reaction conditions, alkenes may undergo either of two types of catalytic polymerization. The products of the first type, which may be termed true polymerization, consist of alkenes having molecular weights which are integral multiples of the monomer alkene. The second type, conjunct polymerization, yields a complex mixture of alkanes, alkenes, alkadienes, cycloalkanes, cycloalkenes, cycloalkadienes, and, in some cases, aromatic hydrocarbons the products do not necessarily have a number of carbon atoms corresponding to an integral multiple of the monomer. 

P = monoalkene polymerization O = monoalkenc oligomerization X = oxo process D = alkadiene polymerization M = methyl methacrylate polymerization A = 1-alkene polymerization. b Complex unspecified. 

Dienes undergo isomerization due to shifts of the double bonds. The reversible isomerization of allenes to acetylenes is catalyzed characteristically by basic reagents (see Section 4.2.2). Nonconjugated alkadienes tend to isomerize to conjugated alkadienes the conversion is usually accompanied by polymerization. Among other catalysts, activated alumina and chromia-alumina may be used to catalyze the formation of conjugated dienes.89,106-108... 

The properties of a compound with isolated double bonds, such as 1,4-pentadiene, generally are similar to those of simple alkenes because the double bonds are essentially isolated from one another by the intervening CH2 group. However, with a conjugated alkadiene, such as 1,3-pentadiene, or a cumulated alkadiene, such as 2,3-pentadiene, the properties are sufficiently different from those of simple alkenes (and from each other) to warrant separate discussion. Some aspects of the effects of conjugation already have been mentioned, such as the influence on spectroscopic properties (see Section 9-9B). The emphasis here will be on the effects of conjugation on chemical properties. The reactions of greatest interest are addition reactions, and this chapter will include various types of addition reactions electrophilic, radical, cycloaddition, and polymerization. 

The general character of alkene polymerization by radical and ionic mechanisms was discussed briefly in Section 10-8. The same principles apply to the polymerization of alkadienes, with the added feature that there are additional ways of linking the monomer units. The polymer chain may grow by either 1,2 or 1,4 addition to the monomer. With 1,3-butadiene, for example,... 

The polymers of rubber plastics have unsaturated hydrocarbon chain structure, since they are polymerized from alkadienes. The general formula of poly(l,3-butadiene) or butadiene rubber (BR) and polyisoprene or natural rubber (NR) is drawn in Scheme 12.5, where X is hydrogen in BR and methyl group in synthetic polyisoprene or NR. The free radical mechanism of thermal decomposition starts by homolytic scission of the alkyl C-C bonds. Two primary macroradicals (4 and 5) are formed for which the rearrangement... 

The two reactions of vinylsilanes with cycloalkenes and alkadienes discussed above compete with ROMP and ADMET polymerization of the organic parent substances. Scheme 1 has been proposed to combine all the competitive/consecutive reactions. The successful formation of silyldiene and bis(silyl)diene occurs exclusively when n = 4 (see Scheme 1). 

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